In commercial food preparation facilities, such as commercial kitchens and restaurants, the sink can be a major source of water borne food waste. In the course of normal food preparation, food wastes comprising FOG and/or food solids may be inadvertently or intentionally introduced to the waste water drainage system and, in other cases, a mechanical chopper such as a garborator is used to shred the food waste as it leaves the sink and enters the waste water system. Many food preparation establishments, such as commercial restaurants and the like, have multiple sinks for such food waste disposal.
The direct disposal into the sanitary sewer system of FOG and FOG laden debris from commercial food preparation facilities is problematic. There are a number of reasons why this is so, including the tendency for such materials to clog or plug sanitary sewage systems and the difficulty of adequately treating and digesting such materials in a sewage treatment facility. Therefore, many jurisdictions require that these materials be removed from the waste water stream before permitting the waste water stream to be added to the sanitary sewer system. Such removed materials may then be separately disposed of, for example, at solid land fill sites.
Devices known as waste water separators or grease interceptors have been developed to carry out the separation of such food borne wastes from the waste water. These waste water separators are connected to the waste water effluent stream from the food preparation facility and are integrated into the building drain line before the drain line reaches the municipal sanitary sewer system. The interceptor may commonly be located internally within the kitchen or externally adjacent to the building. The grease interceptors may take a number of forms, but typically consist of an in-line container which is mounted on, at or below grade within the waste water discharge system downstream of all of the discharging sinks, appliances and the like. The container typically includes features that are configured to trap FOG which may, for example, float to the surface of the container and trap solids which may sink, while permitting separated or clarified water to pass through to the sewer system. Once enough of the trapped waste FOG and solids have accumulated in the container, the wastes can be physically removed in a periodic pump out or servicing step. The container may also contain features to collect solids for disposal. In this way these wastes are conveniently and continuously removed from the waste water before the waste water enters the sanitary sewer system. While good in theory, in practice such systems pose many challenges. The smell from the trapped wastes can be overwhelming, when the separator is opened for servicing. Having individual pump out trucks to provide periodic service can be expensive as there is a charge associated with each visit.
One identified need is to provide a high efficiency separator using a compact footprint. Secondarily, qualified separation based on independent third party validation can offer comparable operation in respect of maintenance frequency but enhanced separation performance based on hydromechanical features. In some cases such devices may or need to be located outside of the building envelop, saving on internal space and making the servicing access easier. As well, by locating the separators outside of the building footprint, having the unpleasant odours associated with the devices being serviced and pumped out inside the kitchen can be avoided—thereby avoiding having bad smells permeate the interior of the food service establishment. This increases the window of time when servicing can occur as it does not have to wait until the food service establishment is otherwise closed to avoid the bad smells being released inside the premises.
However, locating the separators outside of the building footprint has some issues. For example, waste water drainage lines operate by gravity drainage. Most municipal building codes prescribe a minimum slope for the waste water drainage conduits to ensure the free flow of water waste through the drainage system. Therefore the further from the source of the fluid, such as a sink, the lower in the ground the drain line is likely to be and the deeper the separator has to be buried. Thus often, if the waste water separator is to be located outside of the building footprint, it must be buried a certain amount below the surface grade, and the further away it is the deeper it must be buried, due to the fall in the buried waste water pipe. As well in regions that have ground freezing the waste water pipes will typically need to be buried below the frost line to prevent them from freezing.
Buried vessels must be able to resist the loads that are applied to the vessel during their normal everyday use. In the past such buried vessels have been made out of reinforced concrete structures or epoxy-coated metals which can be used to form rigid containment vessels. Now, it is preferred to use more cost efficient materials and manufacturing methods, such as plastic molding techniques, to reduce the cost of making, transporting and installing such underground vessels. Any such plastic molded vessels need to be strong enough to resisting normal sub grade loading patterns. There are two loading extremes. The first is when the vessel is full of waste water. Fortunately, in this case the load of the water pressing on the side walls may be passed into the soil adjacent to the exterior of the vessel. Thus, in addition to the inherent strength of walls of the vessel there is some load support from the surrounding soil. The other loading extreme comes when the vessel is empty, for example when it is being serviced and the FOG and solid wastes are being pumped out, but there is, for example, a high water table or ground water level on the outside of the vessel. In that case rather than having pressure directed outwardly and supported by the surrounding surface, the pressure is directed upwardly and inwardly on the hollow vessel. Further, depending upon how close to the surface the water table or ground water level is, there may be large upward buoyancy forces generated which will try to push the hollow vessel up out of the ground. Unrestrained movement of the vessel under the influence of such lifting forces can cause misalignment of the fluid connections with the drain lines leading into and out of the vessel leading to leaks and unacceptable ground water contamination.
One prior art design for a large flow through waste water separator is found in U.S. Pat. No. 7,481,321 entitled Interceptor for Separating a Mixture which issued Jan. 27, 2009. In FIGS. 8 and 9 a large throughput volume design is shown which can accommodate flow rates of between 10 gallons per minute and 100 gallons per minute. The device includes top openings to facilitate clean out. The body appears to be narrow at the top, wider at the middle and tapers towards a bottom. Built in lifting handles are provided. U.S. Pat. No. 7,011,752 entitled Waste Water Separator and Method of Using the Same issued on Mar. 14, 2006 and teaches a separator with a ramp molded into the floor to direct the water flow through the body in a diagonal manner to facilitate separation of the FOG. Neither of these prior patents addresses the load bearing problems associated with the buoyancy forces that can arise upon a clean out of a buried vessel where the vessel is buried below the top of the water table. Other prior waste water separator patents include:
U.S. Pat. No. 4,145,287
U.S. Pat. No. 7,011,752
U.S. Pat. No. 7,300,588
U.S. Pat. No. 7,427,356
U.S. Pat. No. 7,481,321
U.S. Pat. No. 7,641,805
U.S. Pat. No. 7,828,960
U.S. Pat. No. 7,967,985
U.S. Pat. No. 7,997,156
U.S. Pat. No. 8,153,004
U.S. Pat. No. 8,252,188
United States Publication No. US2014/0150877